Computer graphics systems have become a common tool in the workplace. Graphic images can be created on the computer display screen by a variety of application and desktop publishing programs. Frequently, the user wishes to create objects such as lines that are evenly spaced as referenced to a ruler, or boxes that butt up against one another. While the lines may appear evenly spaced on the computer screen, they are often not evenly spaced when the image is transmitted to a laser printer. Similarly, boxes that appear to butt up against one another on the screen in perfect alignment are either overlapping or do not touch each other when the image is transmitted to the printer.
The reason for this problem is that computer display screens have a resolution that is substantially less than the resolution of a typical laser printer. A typical computer terminal has a resolution of 72 or 96 dots per inch (dpi), while a typical laser printer has a resolution of 300 dpi or even 600 dpi. The computer system must perform some calculations to translate the image on the low resolution computer screen to the high resolution of the printer. When the user is working in a system that uses inches as the unit of measurement, 96 dpi is a convenient resolution because there is an integral number of video dots per unit of length measurement. For a 96 dpi display there are 6 dots of video display per 1/16 inch. However, if the user has a video terminal with a different resolution, or is working in the metric system or some other scale of measurement, there may not be an integral number of dots per unit of the length measurement used. For example, a video terminal with a resolution of 96 dpi will result in a resolution of 3.78 dots per millimeter if the user is in the metric system. Computer systems round off this value, for purposes of display on the screen, to an integral number of dots per millimeter, with some millimeter intervals represented by 3 dots of video display while other millimeter intervals are represented by 4 dots of video display. When a ruler is displayed on the screen to assist the user in drawing and moving objects, the marks on the ruler which represent the units of length measurement do not have a uniform displayed size. For example, some displayed millimeter marks will be 3 dots apart and others will be 4 dots, and none will be precisely 1 millimeter apart. As a result precise measurement and location of objects on the screen is not possible beyond the screen resolution.
Similarly, when an object is moved from one location on a display screen to a new location, the object will maintain the same size as initially drawn on the display screen but might not seem to be the same size when measured by the ruler. The same unit of length measurement, when measured by the ruler at the new location, may not be represented by the same number of dots. This problem is also encountered when attempting to draw two objects to have the same size at different locations on the display screen when the units of length measurement on the ruler have a different displayed length at the two locations. Although the two objects appear to have the same size when measured by the ruler, they will print out with different sizes. Similarly, if one object is drawn and then moved to the location of another object that is drawn to be the same size as measured by the ruler marks, the two objects will be displayed as having different sizes.
It will, therefore, be appreciated that there is a significant need for a computer system that will allow the user to generate objects on a display screen, move the objects about the screen, and print the objects accurately on a printer. The present invention fulfills these needs, and further provides other related advantages.